1. Field of the Invention
This invention relates, in general, to processes and apparatus for separating hydrocarbon gases into residue gases and less volatile products. More particularly, but not by way of limitation, the invention relates to processes and apparatus for separating gas streams such as natural gas streams into a residue gas fraction containing a major portion of methane and a product fraction containing a major portion of less volatile components.
2. Description of the Prior Art
In the utilization and marketing of natural gas and synthetic gas obtained from coal, oil and tar, it is desirable to separate ethane, propane and less volatile components from methane since the separated ethane, propane and less volatile components are substantially more valuable in their separated state. Processes for separating these components from natural gas are well known. Available processes for separating these materials include refrigeration processes, oil absorption processes, refrigerated oil absorption processes and cryogenic processes. The particular process chosen depends on factors such as plant location, equipment costs, composition of the residue gas and product fractions created, the availability of external energy sources, and other factors.
In a typical refrigeration system of separating a resiude gas from a product fraction, a natural gas feed at pipeline pressure and temperature is first compressed and then refrigerated. Refrigeration is generally accomplished by a closed loop freon or propane system and compressor. Following refrigeration to a phase-separating temperature and pressure, the natural gas is separated into a residue gas and a product liquid. For thermal efficiency, the feed gas moving between the compressor and the refrigerator is pre-cooled by heat exchange with the separated residue gas and product liquid.
The refrigeration processes and other processes for separating natural gas into residue gas fractions and less volatile fractions have not been entirely satisfactory. Particularly, the refrigeration capacity must be designed on the basis of the hottest weather in summer and the highest feed gas temperatures. This often results in an overly expensive refrigeration system and unnecessary refrigeration capacity during the vast majority of the operation time.
Another problem is that the refrigeration equipment or the equipment used in non-refrigeration processes is unnecessarily complicated and expensive to construct or repair. Similarly, such equipment is generally difficult to maintain, especially in remote locations. It is also not capable of adapting to a wide range of operating conditions and must be designed carefully for the appropriate temperatures and flow rates.